Research Of Maritime Evaporation Duct Channel Modeling Based On Parabolic Equation Method

With China’s strategy of building a maritime power and restarting the Maritime Silk Road,as well as the rapid development of marine economy around the world,the coverage rate and quality of maritime communication network have been put forward higher requirements,and the maritime communication field has attracted extensive attention.The weather over the ocean is complicated and changeable,and the surface type is unique.There are many environmental factors affecting the propagation of radio waves,which may lead to abnormal propagation phenomena such as atmospheric duct,which will affect the transmission quality,positioning accuracy and action distance of the communication system,and even lead to its interruption.Evaporation duct is the most common type of atmospheric duct in sea surface environment,which can trap electromagnetic wave in the atmosphere at a certain height,and is an important beyond-line-of-sight propagation mechanism.Therefore,based on the theoretical and simulation analysis of wireless channel transmission characteristics in the evaporation duct environment near the sea,the channel modeling research is carried out to form the evaporation duct channel model,which has important guiding significance for the design and performance evaluation of the beyond-line-of-sight communication system at sea.Parabolic equation method(PEM)is a deterministic model approximated by wave equation,which is often used to predict radio wave propagation in tropospheric environment.PEM can well consider the atmospheric refraction effect,stably and accurately solve the radio wave propagation in the range of line of sight and beyond line of sight,and can accelerate the calculation through fast Fourier transform.It is very suitable for the characteristic prediction and analysis of maritime wireless channel.Based on PEM,this thesis deeply studies the complex environmental factors affecting the characteristics of marine channel,such as rough sea surface and evaporation duct.Starting with large-scale fading and small-scale fading,this thesis establishes the channel model of marine evaporation duct based on electromagnetic simulation and statistical law,and deduces the estimation scheme of its channel capacity,which provides a reference for the application and performance evaluation of marine wireless communication system.The main contents of this thesis are as follows:Firstly,the basic theory of two-dimensional PEM is derived and the beyond-line-of-sight propagation in evaporation duct is simulated.The Wide Angle Parabolic Equation(WAPE)and its Split-Step Fourier Transform(SSFT)solution form were derived from the twodimensional scalar Helmhotlz equation.The initial field and boundary conditions are introduced.Compared with the two-ray model and the four-ray model in the flat ground scenario and the single-edge peak scenario,the correctness of the proposed method is verified.In this thesis,the treatment of PEM lower boundary in wave propagation at sea--two rough sea surface models are studied,and their characteristics are analyzed by numerical examples.Then,the refractive index model and atmospheric absorption model of evaporation duct are studied,and the beyond-line-of-sight propagation conditions of evaporation duct are introduced,and the beyond-line-of-sight propagation of electromagnetic wave in horizontal uniform and horizontal non-uniform evaporation duct is simulated.Secondly,BP neural network is applied to propagation prediction in evaporation duct environment.The path loss(PL)of wave propagation in the evaporation duct is regarded as the output,and the factors affecting PL,such as signal frequency,receiving position,duct parameters and sea surface wind wave,are regarded as the inputs.Firstly,a reasonable network structure and hyperparameter configuration are designed,and then the learning data obtained by PEM are used to train the network.Finally,a BP neural network model with similar prediction accuracy but higher computational efficiency to PEM is obtained.Thirdly,a modeling method and capacity estimation scheme of evaporation duct beyondline-of-sight channel are proposed.Based on PEM or BP neural network,the large-scale fading mechanism of electromagnetic wave propagating along the surface evaporative duct channel is characterized,and the small-scale fading mechanism is characterized by statistical characteristics.A hybrid evaporation duct channel model based on electromagnetic simulation and statistical law is formed,and the channel capacity estimation scheme is deduced.The electromagnetic modeling of the real sea surface propagation environment is carried out to calculate the path loss distribution and the channel capacity of the multi-antenna system in the evaporation duct environment,and to quantify the B-Lo S propagation performance improvement caused by MIMO technology.